Today, caching is an integral part of the Internet infrastructure—it is extensively deployed for many different reasons. For example, caching is used to reduce bandwidth costs, share server costs, or increase response speed. There exist numerous caching technologies: browser caching, content distribution network, push caching, adaptive caching, active caching, streaming caches, etc.
Caching is important to network service providers (NSPs) and multiple-system operators (MSOs), which provide fixed or mobile broadband bandwidth to retail customers. For these providers, reducing customer churn rate is a major business driver. One way to reduce churn rate is to enhance user experience through caching.
Most NSPs and MSOs own a bandwidth infrastructure, which is both an asset and a liability—operating the infrastructure consumes working capital. As they have sunk significant capital in building up the infrastructure—it is to their advantage to leverage their existing infrastructure.
From the cost perspective, server and storage costs have dropped relative to bandwidth costs. The reason is that bandwidth costs are tied to the physical distance between a transmitter and a receiver. In contrast, the costs of computing and storage have decreased exponentially as the relevant technologies have made continuous improvements. However, the costs of laying cables and maintaining the ground lease for cell towers have actually risen over the years along with the general inflation.
Therefore, caching is a way to substitute the more expensive bandwidth resources with the less expensive computing and storage resources, while still improving the performance of content access in an average sense.
For NSPs, 2 user-experience metrics are important: (1) response speed of interactive applications, and (2) throughput of large-file applications. For interactive applications such as web browsing, the user is most concerned with the speed that a web page is rendered. For large-file applications such as video streaming, the user is most concerned with the speed that the video buffer is filled, which directly translates into the download throughput. Caching will help both types of application.
In the current solutions for web caching, cache nodes (devices that implement caching) are not placed in access or backhaul networks. Instead, cache nodes are placed in data centers or hub locations. The reason for doing this is that cache nodes are servers that need a protected environment. To expose a server in an outdoor environment, the server has to be ruggedized to withstand high temperature, rain, and other weather-related impacts.
However, as the server technologies have improved, it is now economical to place ruggedized cache nodes even in an outdoor setting such as the cell transmission tower of a mobile carrier, or the street cabinet (or local multiplexer) of a cable system operator. These outdoor locations are in the access or backhaul network of an NSP or MSO.
Placing cache nodes at such locations brings new technical challenges. For example, in a mobile carrier network, a user can move from one cell to the next. Once a user moves, the user device changes its network attachment point—the mobile carrier has to perform handoff by rerouting the packets to a different location. The handoff process breaks content caching at the cell towers as caching is tied to TCP (transmission control protocol) termination.
In TCP termination, packets destined for either the mobile device or the server must traverse the termination point. But once the mobile device changes its network attachment point, packets destined for either the mobile device or the server may not pass through the termination point anymore. The termination point has to be relocated. Preferably, the cache content associated with the mobile device is also relocated to the same place.
For MSOs and fixed-line NSPs, there are no mobility (handoff) issues. However, for all NSPs and MSOs, caches installed in access or backhaul network nodes are serving a highly restricted group of users; the cache content should be optimized with this in mind.
Therefore, there is a need to improve caching by moving cache nodes to the access or backhaul networks of NSPs and MSOs. The new type of cache nodes has to be optimized for handoff and serving a highly restricted group of users.